Selenium

Place it wherever you like. Probably makes sense be system level rather than project level.

Confirm that it works by running in a new terminal session: java -jar PATH-TO-SELENIUM.jar
There should be a message like "RemoteWebDriver instances should connect to: http://127.0.0.1:4444/wd/hub".
Confirm that that page loads. Quit by using CTRL-C in terminal.